title: Protein folding dynamics of cytochrome c seen by transient grating and transient absorption spectroscopies.
abstract: We investigate optically triggered protein folding dynamics of cytochrome c (Cytc) using transient grating (TG) and transient absorption (TA) spectroscopies. Despite many studies on protein folding dynamics of Cytc, a well-known model protein, direct spectroscopic evidence for the three-dimensional global folding process has been rarely reported. By measuring the TG signal of CO-bound Cytc (Cytc-CO) in the presence of a denaturant, we clearly detected the change of diffusion coefficient that reflects the size change of Cytc upon photodissociation of the CO ligand from unfolded Cytc-CO. The quantitative analysis of TG signals supports that the optically triggered folding reaction of Cytc in the presence of a denaturant takes place through a detectable intermediate (three-state folding kinetics). This is in contrast with the two-state folding dynamics of Cytc under a denaturant-free environment without any detectable intermediate. (1) From the quantitative global analysis of the TG signals, the rate constants for the U → I and I → N transitions in a CAPS buffer solution (pH 7) at room temperature in the presence of a denaturant at various concentrations are determined to be 1065 ± 17 to 3476 ± 103 s(-1) and 101 ± 6 to 589 ± 21 s(-1), respectively. In addition, the activation energies (E(a)) for the U → I and I → N transitions are determined to be 8.7 ± 1.0 kcal/mol and 7.1 ± 1.3 kcal/mol, respectively. The folding dynamics of Cytc initiated by the CO photolysis is discussed based in terms of the protein size change.
authors.affiliation: Center for Time-Resolved Diffraction, Department of Chemistry, Graduate School of Nanoscience & Technology (WCU), KAIST, Daejeon, Republic of Korea. cjkbabo@gmail.com
authors.forename: Jungkweon
authors.initials: J
authors.lastname: Choi
authors.forename: Cheolhee
authors.initials: C
authors.lastname: Yang
authors.forename: Jeongho
authors.initials: J
authors.lastname: Kim
authors.forename: Hyotcherl
authors.initials: H
authors.lastname: Ihee
mesh_terms: D000042:Absorption; D000818:Animals; D002248:Carbon Monoxide / Q000378:metabolism; D045304:Cytochromes c / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D008024:Ligands; D008958:Models, Molecular; D055620:Optical Phenomena; D010084:Oxidation-Reduction; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D013057:Spectrum Analysis
chemical_list: D008024:Ligands; D002248:Carbon Monoxide; D045304:Cytochromes c